Digital dermatitis (DD) has been a problem in dairies for a long time and is becoming more prevalent in beef cattle, says Terry Engelken, a professor in the College of Veterinary Medicine at Iowa State University.
Also known as “hairy heel warts” or “strawberry foot rot," DD lesions are generally at the back of the foot, between the dewclaws and the coronary band. It starts as a small erosion and works its way into the deeper tissues. The chronic, classical sign – where it gets the name hairy heel wart – is deep erosions and proliferative hairlike tissue growing out from those areas.
“In feedyards that have it, DD is rapidly becoming the most common cause of lameness,” Engelken says. “Foot rot and other foot problems are pretty straightforward in terms of intervention. DD is much more difficult to prevent and treat."
Not all cattle are lame at first, so it’s hard to diagnose early. By the time cattle are lame, there are many more with early lesions that will become lame later, Engelken says. It can occur in outdoor pens, bedded packs, indoor facilities or slatted floors.
Causes and signs to watch for
There has to be some kind of initial trauma to the skin for DD to occur. Pen conditions might be a factor, at least in the initial outbreak. If pens are wet or frozen – with rough spots – skin may be damaged. Many of the organisms found in these lesions are unable to penetrate intact, healthy skin.
DD is caused by multiple bacteria working together. “We’ve always talked about treponema as causing DD, but what we find in early lesions are other bacteria,” Engelken says. “The treponema come in later and become the dominant bacterial family in chronic cases.”
Matt Miesner, a clinical professor and section head of livestock services in Kansas State University’s College of Veterinary Medicine, says this disease is diagnosed with a biopsy of the lesion. Treponema, a spirochete (spiral-shaped bacteria), can be seen under a microscope.
“The disease itself is multifactorial. It may take several factors working together for cattle to become susceptible; first, [there is] something that breaks down the skin barrier to allow bacteria access. Secondly, there are a host of other bacteria that help it along, irritating the skin, enabling the spirochete [to] dig in,” Miesner says.
DD often become proliferative and may look warty – bulging out with fingerlike projections. Miesner says it is painful when it becomes ulcerative. “When it gets between the heel bulbs, you’ll see the animal standing with the toe down and heel lifted to take pressure off the painful heel area,” he says.
There is often swelling, but not as much as seen with foot rot. Swelling rarely moves up the foot unless there is a secondary infection. “For diagnosis, we look at the foot, and if there are lesions on the haired skin between the heel bulbs or on the front part of the foot, it’s not foot rot. It’s more likely to be DD,” Miesner says.
Depending on how bad the lesions are, there may be reduction in average daily gain of 0.15 to 0.25 pound per day in animals not treated with a footbath. Engelken adds, “If an animal’s daily gain is reduced by 0.25 pound over a 200-day feeding period, this would be [over] 40 pounds."
Treatment and prevention
DD does not respond to systemic antibiotics and instead, must be treated topically. Thus, it is important to properly diagnosis this condition rather than simply treating it like foot rot. Engelken says that putting a wrap on the foot with tetracycline or other antibiotics works for individual animals but is impractical for a whole pen of lame animals.
“Usually, we run them through a footbath. Most commonly the solution used is 5 to 10 percent copper sulfate, or 5 to 10 percent formaldehyde or formalin solution,” Engelken says. “Some yards run all cattle through upon arrival and again at reimplant time. Even with this protocol for prevention, most yards also include additional treatments on a pen-by-pen basis when they start to see lameness. Some yards regularly schedule it every 30 days; each pen goes through the footbath. It depends on severity of the problem, number of cattle and what they’ve put together for a treatment plan with their veterinarian, in terms of what seems to work.”
With all the bacteria in these lesions, Engelken says finding the right combination to put in a potential vaccine would be difficult. Instead, research is looking at other things such as bedding pack treatments that reduce the pH in the material (to inhibit bacteria and keep the pen drier). A box scraper can knock off sharp edges in outdoor pens.
Dorte Dopfer, an associate professor of food animal production medicine at the University of Wisconsin, has found that footbath chemicals can sometimes be detrimental. Copper sulfate is often used, but if the footbath becomes extremely acidified (below a pH of 3) it becomes caustic and irritates inflamed surfaces even more. This results in more proliferation of hairy heel warts and a higher risk for outbreaks and recurrence of lesions. “This is why people think the ‘bugs’ have become resistant and footbaths are not working anymore for disinfecting the feet,” she says.
Her advice is to customize frequency and concentration of footbaths to the dynamics of DD on the farm. “We monitor emergence and occurrence of proliferative, chronic ulcerative lesions and give advice regarding whether the footbath strategy and topical treatment protocols are optimal,” she says.
Her lab offers a service to take samples of footbath solutions at zero, 50 and 100, or how many cows walk through it, and culture that fluid. If there are more than 100,000 microbes per milliliter, the fluid should be changed.
She just completed research in which DD was experimentally induced in Holstein steers, using lesions to infect healthy cattle, to see how this disease evolves and the benefit of prevention and control.
Tests can be done to check for DD. When treponeme bacteria make contact with the blood, there are antibodies formed that can be measured with an enzyme-linked immunosorbent assay (ELISA) test. “We’ve also developed a DD check app to record DD lesions so we can go on-farm and type in what we find in terms of stages of DD,” Döpfer says.
Artificial intelligence can detect DD lesions early – with cameras at floor level or close to chutes – to detect DD and make automated records in a spreadsheet that can be sent to a hoof trimmer or producer to begin treatment. In the near future, camera models could work on tablets and mobile phones.